In recent years, use of a multilayer structure for semiconductor devices has been increasingly growing due to an increase in pattern density of the semiconductor devices. In order to manufacture the semiconductor device of the multilayer structure, it is necessary to perform a process of planarization during manufacture of the semiconductor device. To this end, one of most widely used techniques in the art is a chemical mechanical polishing (CMP) process. In the CMP process, with a polishing pad brought into close contact with a surface of a wafer on which steps are formed, slurries are supplied between the polishing pad and the surface of the wafer to polish the surface of the wafer with polishing abrasives contained in the slurries, thereby obtaining a flattened surface of the wafer. An apparatus for performing the CMP process generally comprises a carrier to hold the wafer, the polishing pad, a rotational table to support the polishing pad, and the like.
FIG. 1 is a constructional view of a conventional chemical mechanical polishing apparatus showing a top surface and a cross-section of the CMP apparatus.
Referring to FIG. 1, the conventional CMP apparatus comprises a carrier 110 to hold a wafer (not shown), a polishing pad 120 to mechanically polish the surface of the wafer via friction with the wafer, and a rotational table 130 to support the polishing pad 120 while rotating for efficient polishing of the wafer. On the polishing pad 120, slurries and other materials are supplied for chemical mechanical polishing of the wafer.
In the CMP apparatus, while the carrier 110 rotates or moves upward or downward, the wafer held by the carrier 100 is brought into contact with the polishing pad 120 and the slurries so that the surface of the wafer is polished. Meanwhile, with the conventional CMP apparatus having the above structure, abrasion is likely to concentrate on a specific region “a” of the polishing pad 120, causing the polishing pad 120 to be compressed at various rates different from locations on the polishing pad 120 where the abrasion occurs at different degrees. As a result, not only the surface of the wafer is non-uniformly polished, but also a replacement cycle of the polishing pad 120 is shortened, thereby increasing the manufacturing costs while deteriorating a quality of the process. In FIG. 2, this phenomenon of the conventional CMP apparatus is shown in detail.
FIG. 2 is a cross-sectional view showing a polishing process using a conventional CMP apparatus.
Referring to FIG. 2, a polishing pad 220 is brought into close contact with a wafer 215 under pressure by a carrier 210 in a condition that the polishing pad 220 is subjected to various compression rates resulting from different degrees of abrasion depending on locations of the polishing pad 220.
In other words, on the polishing pad 220, a compression rate at Part B side which is less abraded than Part C side is higher than the Part C side which is more abraded than the Part B side. In this regard, it is required to provide a technique which can prevent or compliment non-uniform contact pressure between the wafer 215 and the polishing pad 220 due to the different compression rates on the polish pad 220. Reference numeral 230 indicates a rotational table which holds and supports the polishing pad 220.